The invention relates to equipment providing physiological protection of aircraft pilots against the effects of height and accelerations.
Protection against the effects of height is currently ensured by a source of respirable oxygen connected, through a pressure reducing valve and a conduit, to an oxygen mask applied as hermetically as possible to the face of a pilot.
Protection against the effects of accelerations is ensured by a suit known as anti-g and by an oxygen overpressure applied inside the mask.
Moreover, the operation of these means of protection supposes the presence of a detector of longitudinal acceleration, generally with a runner, compared to the pilot's body, and of a valve known as anti-g located on a source of compressed gas. This source is currently the respirable oxygen reserve.
The anti-g suit comprises a jacket and trousers. These two elements comprise bladders connected to pipings. The piping of the trousers bladders is connected to the anti-g valve, and the piping of the jacket bladders is connected to a valve supplying the respirable oxygen mask.
The operation is as follows. In case of movement of the aircraft causing a longitudinal acceleration directed from the head to the feet of the pilot, the accelerometer with runner causes the progressive opening of the anti-g valve and of the overpressure setting valve of the oxygen mask.
The opening of the anti-g valve causes the inflation of the trousers bladders, thus applying to the pilot's lower limbs a pressure preventing the accumulation of blood in the veins. The opening of the oxygen overpressure valve causes an overpressure to the mask and jacket. The internal respiratory overpressure induced in the mask, and consequently inside the pilot's chest, is compensated by the external overpressure on the pilot's chest induced in the jacket bladders. To avoid lesions, the internal and external pressures must remain equal.
The current equipment has many drawbacks. Since respirable oxygen is used as the agent of inflation, materials compatible with oxygen must be used; these materials age badly, and it is necessary to renew them often. In case of fire, the presence of oxygen in contact with the body of the pilot increase the risk and the seriousness of burns. Further, should the jacket be torn, oxygen is unable to reach the mask.
The efficiency of the jacket supposes an adjustment on the pilot's chest and an oxygen flow able to compensate the variations of volume of the rib cage without any delay. These conditions are poorly realized by the current equipment. The current means of protection, which use respirable oxygen as an agent of inflation, increases the consumption of a resource available in limited quantity in the aircraft, and thus might decrease the duration of missions in high altitude. The decreased duration would become drastic when the trousers or the jacket are torn. In that case, moreover, fire hazards are increased as oxygen is spread through the cabin.
The current means also does not allow a good use of the oxygen laws of dilution according to the acceleration. Indeed, since the jacket is in series with the pilot's mask, its dead volume prevents the oxygen concentration from moving inside the mask simultaneously toward the exit of the regulator. Then, when the aircraft climbs rapidly, the oxygen content inspired in the mixture is insufficient, which is not acceptable for pilot safety.
In addition, in case of failure of the anti-g valve, the respiratory overpressure is not ensured any longer. The moment when the bladders are intended to be inflated for protecting the pilot against accelerations is delayed because of the inertia of the sensor (runner) and equipment (anti-g valve, trousers), thus reducing the efficiency of the pilot protection. The trousers are inflated abruptly and uniformly, which is very uncomfortable for the pilot who feels a punch and responds unsatisfactorily to the laws of balance between the blood pressure generated by the acceleration and the backpressure exerted by the anti-g trousers. In addition, the uniform inflation has an adverse effect on the blood return to the heart.